For many years, automobiIes have employed catalytic converters in their exhaust systems for the treatment of combustion gases of the internal combustion engine. These catalytic converters are employed to reduce the carbon monoxide, unburned hydrocarbon and nitrogen oxide content of the exhaust. In most if not all instances, noble metal catalysts have been employed. Platinum, palladium and more recently rhodium have been dispersed on beads or pellets of gamma alumina or dispersed on micron-size particles of an alumina washcoat on the surface of a suitable ceramic or metallic support body such as an extruded cordierite monolith.
Although they are in short supply, the noble metals have been employed in these automotive applications because of their durability at the high temperatures of the exhaust gas and because of their resistance to poisoning by elements such as lead and phosphorus. Many base metals have previously been evaluated and found lacking in these critical characteristics. Various non-noble metal oxides such as the oxides of copper, chromium, nickel, vanadium, iron, zirconium, cobalt, molybdenum and tungsten have shown promising initial oxidation activity with synthetic exhaust mixtures in bench tests. However, they display much lower activity in realistic engine tests that tend to degrade the catalyst.
We have found a specific combination of a base metal oxide(s) and two oxide support materials that cooperate when in the form of a washcoat composition on a support body to overcome many of the shortcomings of the prior art uses of base metal catalysts.